COMPARATIVE BIOLOGY AND PATHOGENESIS OF AIDS AND HEPATITIS-B VIRUSES - RELATED BUT DIFFERENT

AIDS (HIV) and hepatitis B viruses are remarkably similar in their sha ring of reverse transcription, in their ancestral origins and common g enetic elements, and in their modes of transmission. Both are hypermut able and exist as quasispecies due primarily to errors in reverse tran scription, though there is severe restriction in the replicative compe tence of most hepatitis B mutants. They differ in the lack of an integ rase in hepatitis B virus and in their pathogenesis in the infected ho st. EW survives mainly by antigenic variability, immune evasion, and i mpairment of immune function though viral regulatory control elements seek to restrict fatal damage to the host. Hepatitis B virus survives primarily by mutation of e antigen/core genes that directly obviates c ytotoxic T cell destruction of infected liver cells, or indirectly lim its destruction of infected cells through induction of anergy in the c ytotoxic T cell response. Most persons infected with hepatitis B virus recover completely while recovery from HIV infection is rare if ever. Hepatitis B is highly preventable by vaccine while HIV vaccine is sti ll seeking a meaningful immunoprophylactic target. AIDS and hepatitis B represent an extreme example, among the viruses of man, in their clo se similarities but distinct differences. In depth details and perspec tives are presented in this review.